首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2320篇
  免费   177篇
  国内免费   141篇
电工技术   201篇
综合类   272篇
化学工业   66篇
金属工艺   46篇
机械仪表   181篇
建筑科学   51篇
矿业工程   55篇
能源动力   24篇
轻工业   46篇
水利工程   33篇
石油天然气   29篇
武器工业   38篇
无线电   435篇
一般工业技术   108篇
冶金工业   71篇
原子能技术   28篇
自动化技术   954篇
  2023年   8篇
  2022年   25篇
  2021年   33篇
  2020年   31篇
  2019年   23篇
  2018年   25篇
  2017年   22篇
  2016年   49篇
  2015年   54篇
  2014年   72篇
  2013年   85篇
  2012年   114篇
  2011年   131篇
  2010年   128篇
  2009年   161篇
  2008年   216篇
  2007年   309篇
  2006年   247篇
  2005年   197篇
  2004年   177篇
  2003年   147篇
  2002年   89篇
  2001年   85篇
  2000年   49篇
  1999年   20篇
  1998年   12篇
  1997年   19篇
  1996年   16篇
  1995年   11篇
  1994年   11篇
  1993年   14篇
  1992年   7篇
  1991年   6篇
  1990年   4篇
  1989年   6篇
  1988年   2篇
  1985年   5篇
  1984年   2篇
  1983年   2篇
  1982年   3篇
  1981年   3篇
  1980年   2篇
  1979年   3篇
  1978年   1篇
  1977年   3篇
  1976年   2篇
  1975年   2篇
  1963年   1篇
  1962年   1篇
  1954年   1篇
排序方式: 共有2638条查询结果,搜索用时 15 毫秒
71.
Coralyne is a synthetic analog of berberine related to protoberberine-isoquinoline alkaloids. Isoquinoline derivatives and analogs are renowned as potent radiosensitizers with potential medical application. In the present study, we investigated the effect of coralyne on the cell death, cytoskeletal changes and cell cycle progression of irradiated A549 cells. A clonogenic assay revealed that coralyne pretreatment decreased the viability of A549 cells in a time- and dose-dependent manner. Moreover, exposure to coralyne and ionizing radiation (IR) markedly altered the filamentous actin cytoskeletal architecture and integrin-β binding sites of A549 cells. Treatment with 1–25 µM coralyne in combination with 2 Gy of IR significantly reduced the percentage of cells in G2/M phase compared with 2 Gy IR alone. These results indicate that coralyne is a potent radiosensitizing agent that may find an application in medicine.  相似文献   
72.
This paper presents a theoretical and experimental study on two different methods to evaluate the sign of a determinant with integer entries. The first one is a method based on the Gram—Schmidt orthogonalization process which has been proposed by Clarkson [Cl]. We review his algorithm and propose a variant of his method, for which we give a complete analysis. The second method is an extension to n × n determinants of the ABDPY method [ABD+2] which works only for 2 × 2 and 3 × 3 determinants. Both methods compute the sign of an n× n determinant whose entries are integers on b bits, by using exact arithmetic on only b +O(n) bits. Furthermore, both methods are adaptive, dealing quickly with easy cases and resorting to full-length computation only for null determinants. Received December 30, 1996; revised September 16, 1998.  相似文献   
73.
Using a fixed point relation based on the logarithmic derivative of the k-th order of an algebraic polynomial and the definition of the k-th root of a disk, a family of interval methods for the simultaneous inclusion of complex zeros in circular complex arithmetic was established by Petković [M.S. Petković, On a generalization of the root iterations for polynomial complex zeros in circular interval arithmetic, Computing 27 (1981) 37–55]. In this paper we give computationally verifiable initial conditions that guarantee the convergence of this parallel family of inclusion methods. These conditions are significantly relaxed compared to the previously stated initial conditions presented in literature.  相似文献   
74.
Explanations of working memory span in children were studied in a longitudinal follow-up of J. N. Towse, G. J. Hitch, and U. Hutton (1998). Reading span and operation span were lower when within-task retention intervals were lengthened. For each task, variation in span between test waves and age cohorts was systematically related to changes in processing speed. The two spans explained substantial shared variance in both reading and arithmetic scores, with some evidence for domain specificity. Combined span scores predicted unique variance in scholastic attainment over a 1-year interval. The authors concluded that working memory span is constrained by rapid loss of active codes and is not simply a measure of capacity for resource sharing. Working memory is also implicated in scholastic development. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
75.
信号处理是目前电子战技术发展的一个关键技术。不能单纯从信号处理本身来考虑如何实现信号处理 ,必须从系统角度设计信号处理 ,同时结合工作实践对信号处理提出一些建议。  相似文献   
76.
We describe a vectorized algorithm for an interval arithmetic Newton-like method for a class of systems of nonlinear equations arising from discretizations of nonlinear elliptic PDE. This method converges to a solution under relatively weak conditions. It is founded on a combination of a Newton-like interval method and interval arithmetic ‘fast’ direct solver. In the present paper we focus our attention on aspects of the vectorization, in particular that of a simulation of an interval arithmetic and that of the direct solver.  相似文献   
77.
It has been observed by many researchers that systolic arrays are very suitable for certain high-speed computations. Using a formal methodology, we present a design for a single simple programmable linear systolic array capable of solving large numbers of problems drawn from a variety of applications. The methodology is applicable to problems solvable by sequential algorithms that can be specified as nested for-loops of arbitrary depth. The algorithms of this form that can be computed on the array presented in this paper include 25 algorithms dealing with signal and image processing, algebraic computations, matrix arithmetic, pattern matching, database operations, sorting, and transitive closure. Assuming bounded I/O, for 18 of those algorithms the time and storage complexities are optimal, and therefore no improvement can be expected by using dedicated special-purpose linear systolic arrays designed for individual algorithms. We also describe another design which, using a sufficient large local memory and allowing data to be preloaded and unloaded, has an optimal processor/time product.An earlier version of this paper was presented at Supercomputing '88.This work was partially supported by ONR under the contract N00014-85-K-0046 and by NSF under Grant Number CCR-8906949.  相似文献   
78.
J. L. Schonfelder 《Software》1989,19(6):529-551
The next revision of the standard Fortran language, commonly referred to as Fortran 8x, has now been published, at least in draft form. It is therefore possible for some of its new features to be investigated and the type of programming that can be expected when implementations appear to be explored. This paper looks at the scope provided by the proposed new features for 'semantic extension' of the language. The capability is illustrated by way of example code which could provide an extended-precision numeric facility if implemented. The new linguistic constructs that permit this type of approach to software provision are described as they are used.  相似文献   
79.
针对当前专用RS422设备不能直接移植到AT91RM9200上的问题.利用AT91RM9200芯片上的USART模块,设计开发了RS422高速串行通信模块及其硬件接口电路,并设计了该模块的软件。文中通信模块软硬件的设计.解决了RS422在AT91RM9200上直接移植的问题。在本通信模块的软件设计中,引入了快速CRC冗余校验算法,极大地降低了误码率,提高了通信的可靠性。目前该模块已成功应用于某型导弹导引头等效器的设计中。  相似文献   
80.
探讨了抽油机平衡度与抽油机系统效率的影响关系,同时分析了抽油机平衡调整的本质和终极目标,提出了一种新的抽油机平衡调整方法——通过对电机功率曲线进行付立叶分析而确定平衡块重心位置的方法。在现场对47口抽油机电机功率曲线进行付立叶分析后实施了调整措施;系统效率提高了3.05%,达到了油田增产降耗、延长系统使用寿命、降低操作成本的目的。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号